<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		@media screen and (max-width: 768px){
			html {
				font-size: 62.5%;
			}
		}
		@media screen and (min-width: 768px){
			html {
				font-size: 100%;
			}
		}
		h1{
			font-size: 1.6rem;
		}
	</style>
</head>
<body>
	<h1>hello world!</h1>
	<img src="px与em转换.jpg" alt="">
</body>
</html>